Synthetic Rock Research Articles

Size-Dependent Mechanical Properties and Excavation Responses of Basalt with Hidden Cracks at Baihetan Hydropower Station through DFN–FDEM Modeling

Basalt is an important geotechnical material for engineering construction in Southwest China. However, it has complicated structural features due to its special origin, particularly the widespread occurrence of hidden cracks. Such discontinuities significantly affect the mechanical properties and engineering stability of basalt, and related research is lacking and unsystematic. In this work, taking the underground caverns in the Baihetan Hydropower Station as the engineering background, the size-dependent mechanical behaviors and excavation responses of basalt with hidden cracks were systematically explored based on a synthetic rock mass (SRM) model combining the finite-discrete element method (FDEM) and discrete fracture network (DFN) method. The results showed that: (1) The DFN–FDEM model generated based on the statistical characteristics of the geometric parameters of hidden cracks can consider the real structural characteristics of basalt, whereby the mechanical behaviors found in laboratory tests and at the engineering site could be exactly reproduced. (2) The representative elementary volume (REV) size of basalt blocks containing hidden cracks was 0.5 m, and the mechanical properties obtained at this size were considered equivalent continuum properties. With an increase in the sample dimensions, the mechanical properties reflected in the stress–strain curves changed from elastic–brittle to elastic–plastic or ductile, the strength failure criterion changed from linear to nonlinear, and the failure modes changed from fragmentation failure to local structure-controlled failure and then to splitting failure. (3) The surrounding rock mass near the excavation face of underground caverns typically showed a spalling failure mode, mainly affected by the complex structural characteristics and high in situ stresses, i.e., a tensile fracture mechanism characterized by stress–structure coupling. The research findings not only shed new light on the failure mechanisms and size-dependent mechanical behaviors of hard brittle rocks represented by basalt but also further enrich the basic theory and technical methods for multi-scale analyses in geotechnical engineering, which could provide a reference for the design optimization, construction scheme formulation, and disaster prevention of deep engineering projects.

Numerical stability assessment of a mining slope using the synthetic rock mass modeling approach and strength reduction technique

Numerical stability assessment of a mining slope using the synthetic rock mass modeling approach and strength reduction technique

Effect of load frequency and amplitude of displacement on soft synthetic rock joints under cyclic shear loads

Effect of load frequency and amplitude of displacement on soft synthetic rock joints under cyclic shear loads

Experimental investigation of tunnel damage and spalling in brittle rock using a true-triaxial cell

Deep underground excavations in brittle rocks are subject to several ground stability hazards such as spalling and rockburst. These hazards are typically associated with brittle failure mechanisms for hard and massive rock mass. In this study, an experimental investigation has been carried out to evaluate the mechanisms underlying these induced hazards in deep underground excavations. The main objective of this study is to investigate the behavior of a freshly excavated circular unsupported tunnel in a brittle synthetic rock with a focus on induced damage and spalling response. The experiment used a miniature tunnel boring machine (TBM) to excavate a tunnel in a cubical specimen placed in a true-triaxial cell. The material selected for this experiment was a reproducible synthetic rock analogous to sandstone with brittle characteristics. In the experiment, the specimen was loaded with increasing confining stress under incremental isotropic conditions in the true-triaxial cell until the tunnel failed. Macro-photography was utilized to verify the excavation damage zones and failure mechanisms around the tunnel boundary. The main observed failure mechanism of the model tunnel was spalling, which occurred due to brittle failure and a sudden stress release at the tunnel excavation boundary. In addition to spalling, three zones of damage were identified by macro-photography in the tunnel due to damage from construction, fracturing, and plastic rock deformation. The outcomes point to a unique and in-depth comprehension of how damage and spalling failure during underground excavation develop and its impact on tunnel stability.

Fractal evolution characteristics of fracture meso-damage in uniaxial compression rock masses using bonded block model

With regard to deep mining in metal mines, an investigation into the failure mode of deep fractured rock masses and their corresponding acoustic emission signal characteristics is conducted via uniaxial compression tests. Subsequently, a fractal damage renormalization group mechanical model is developed to explain the behavior of those fractured rock masses. Employing the bonded block model (BBM) numerical simulation method, fracture process in synthetic rock samples is analyzed, thereby validating the efficacy of the mechanical model. The numerical simulations highlight the critical role of fractures expansion in underlying the deterioration of rock mass strength. As the peak load decreases, the fracture fractal dimension increases, leading to a significant 14.2% reduction in compressive strength accompanied by an approximate 8.7% rise in average fracture fractal dimension. A comparative analysis of tetrahedral and voronoi block synthetic rock samples reveals the tetrahedral block samples exhibit a superior ability to depict the fracture behavior of fractured rock masses. Specifically, they offer a more accurate simulation of acoustic emission characteristics and failure modes. Furthermore, variations in the fracture fractal dimension with respect to the hole defect’s position are observed, with the maximum value occurring along the vertical axis of the hole defect. This observation underscores the potential utility of visually monitoring deep rock fracture dynamics as an effective mean for quantitatively evaluating fracture damage and strength degradation in deep rock formations.

Abstract Mo124: New Rho-kinase Inhibitor Reduces Diastolic Dysfunction induced by Estrogen Depletion in Spontaneously Hypertensive Rats

Heart failure with preserved ejection fraction (HFpEF) observed in women with estrogen depletion is a consequence of the reduction of cardioprotection and endothelial dysfunction. Rho-kinase (ROCK) signaling pathway plays a role in cardiac dysfunction consequent to female aging. This work investigated the effects of a new synthetic ROCK inhibitor (iROCK) after oral administration in spontaneously hypertensive rats (SHR) submitted to oophorectomy (OVX). Experimental protocols were approved Animal Care and Use Committee at Universidade Federal do Rio de Janeiro. Under ketamine (80 mg/kg, i.p.) and xylazine (15 mg/kg, i.p.) anesthesia, female SHR submitted to OVX had cardiac function assessed after 8 weeks and compared to SHR-Sham. Eight weeks after OVX, SHR were randomly divided in groups, which were orally treated with either vehicle (DMSO) or iROCK (10 mg/kg) during 2 weeks. Novel iROCK displays potent inhibitory activity for ROCK1 and ROCK2 isoforms, with IC50 of 1.3 μM and 1.7 μM, respectively. At the end of treatment, hemodynamic parameters were evaluated using echocardiography and LV catheterization. Cardiac tissues collected for determining the expression of mitogen-activated protein kinases p38MAPK and extracellular signal-regulated kinase (ERK-1/2) using Western blot technique. After 8 weeks of estrogen depletion, SHR displayed HFpEF because ejection fraction (EF) was 85.2 ± 0.9%, while a reduction in EF from 83.0 ± 2.7 to 64.9 ± 0.9% was only detected after 12 weeks of OVX. Altered filling pressure confirmed the diastolic dysfunction after OVX, because the ratio of rapid mitral flow (E) to rapid wave of mitral annulus tissue Doppler (e') increased from 12.1 ± 1.3 in SHR-Sham to 19.3 ± 0.5. LV end diastolic pressure (LVEDP) increased from 13.4 ± 1.3 to 21.1 ± 4.9 in SHR after 8 weeks post-OVX. Oral administration of iROCK (10 mg/kg) reduced both E/e’ to 16.2 ± 0.5 and LVEDP to 6.4 ± 0.7 mmHg. OVX in SHR increased cardiac p38 MAPK and ERK-1/2 contents by 2.3 and 1.3 fold from SHR-Sham values. In contrast, iROCK reduced p38 overexpression but not altered ERK-1/2 content. Since pro-inflammatory cytokines and oxidative stress activate p38, the recovery of its expression after treatment, indicates that iROCK could reduce the inflammatory component of HF. In conclusion, the new iROCK recovered LV diastolic function induced by estrogen depletion in SHR, through the reduction of myocardial inflammation.

Study of the contact angle and roughness effects on mercury intrusion porosimetry (MIP) analysis in natural/real carbonate rocks using massive pure minerals and synthetic carbonate rocks

Studying pore networks in rocks is critical for understanding reservoir properties, with mercury intrusion porosimetry (MIP) being a key laboratory method. MIP involves capillary intrusion of mercury, with intrusion pressure (P) related to capillary diameter (d) by the Washburn equation, incorporating mercury properties like contact angle (θ) and surface tension (γ). While a constant contact angle of 140° is typically assumed for MIP, it can vary based on rock mineralogy and surface roughness. This study aims to analyze how contact angle variations and surface roughness affect MIP analysis of carbonate rocks. Initially, contact angle data was obtained for calcite, dolomite, and quartz with varying roughness levels. Synthetic rocks were then constructed using these minerals. MIP was performed using the typical 140° contact angle and a calculated contact angle from the Cassie model, which considers surface composition fraction. Natural rock MIP analysis followed, with contact angles varying due to mineral composition and roughness. The study found higher contact angles than the standard 140°, affecting pore size distributions up to 30%. Natural rock pore network curves were adjusted based on synthetic rock data analysis. These findings emphasize the need for accurate contact angle selection in MIP for precise pore distribution analysis and contribute to the further study of carbonate rocks.

The effects of water content on mineralogical and drainage quality dynamics in weathering mine waste rock

Water content plays a critical yet ambivalent role in the physical and geochemical stability of mine tailings and waste rock, but its effects on individual chemical weathering reactions (dissolution and precipitation) and bulk water quality remain poorly understood. We experimented with synthetic waste rock to quantitatively reconcile modal and textural mineralogical parameters (mineral size, association, and liberation) with leachate quality at different water saturation levels (5–100%). Leachate pH consistently decreased from a 13-week average of 6.14 at 100% saturation to 5.37 at 5% saturation. Simultaneously, mineralogical analyses revealed a reduction in the size of carbonate phases over the course of weathering, decreasing from 200 µm to 145 µm as water saturation increased from 5% to 100%, which could be a contributing factor to more alkaline pH in samples with higher water saturation. Total concentrations of iron (Fe) and copper (Cu) in solution increased with lower moisture, with Cu concentrations increasing 24-fold in samples at 5% saturation compared to full saturation. In contrast, arsenic (As) concentration increased with higher moisture levels, which we attribute to reduced galvanic protection of As-bearing pyrite from oxidation. Multivariate statistical evaluation allowed us to uncover correlations between water chemistry and mineralogical data (i.e., sulfide associations or phase perimeters) and to explain chemical differences between samples, particularly those at 100% and 5% water saturation. Our findings underscore the importance of conducting quantitative mineralogical investigations on mine waste materials and considering their stored water content in the formulation of mine waste management strategies.

Production of Synthetic Carbonate Rocks Using Limestone Mining Waste: Mineralogical, Petrophysical and Geomechanical Characterization

Production of Synthetic Carbonate Rocks Using Limestone Mining Waste: Mineralogical, Petrophysical and Geomechanical Characterization

Investigation of petrophysical properties of synthetic carbonate plugs: Adding a novel 3D printing approach to control pore networks

The physical and chemical properties of rocks play a crucial role in understanding fluid-solid flow behavior at the pore level. Thus, studying pore space characteristics is important in evaluating and determining petrophysical properties of various rock types, including synthetic rocks, which can be designed to mimic natural rocks. This study investigates the petrophysical properties of synthetic carbonate plugs by using a new approach that correlates the base material and a 3D printing solution with porosity and permeability. The research shows that with precise particle size and morphology, pure mineral materials such as calcite, dolomite, quartz and a non-structural Portland cement may produce a controlled rock matrix. The synthetic plugs developed in this study exhibit controlled macro, meso, and micro porosities, including fractures and vuggys, by the solubilization of materials with controlled morphology by 3D printing, which provides valuable information on regulating pore space in synthetic carbonate rocks.

Experimental and theoretical analysis of finely bedded porous rock models with internal cracks

The behavior of ultrasonic waves in synthetic rocks consisting of alternating layers of sand-based (porous and permeable) and acrylic (unporous) materials is investigated. Two synthetic layered media are created, one without cracks and the other with parallel cracks in one of the layers, to increase anisotropy and simulate a heterogeneous transversely isotropic medium with a vertical axis of symmetry. Microcomputed tomography is used to obtain images of the samples, which indicate that there are no bubbles present and that the layers are well connected without any gaps or breaks. The experiment uses ultrasonic measurements to determine the propagation of P and S waves, with transducers at frequencies of 100 kHz, 500 kHz, and 1 MHz for traveltime and waveform measurements. These three sources are chosen to verify the effective behavior of the samples, which depends on the relationship between the dominant wavelength of investigation and the layer thickness ([Formula: see text]). The measured velocities are compared with theoretical models based on Backus, Kennett (traditional models), and Backus (modified for cracked media by Schoenberg and Muir’s theory). The main finding is that the cracked medium exhibits at least twice as large a difference in behavior for P- and S-wave vertical velocities as a function of the number of layers compared with the uncracked medium.

Chromium sorption on synthetic and natural rock minerals with emphasis on speciation behavior and kinetic model using Cr51

Abstract The presence of chromate in the aquatic environment poses toxicity and pollution to the environment. Therefore, the needs to establish methods to get rid of this species is a must. The effect of different natural rock minerals; pyrite, magnetite, pyrrhotite, and wurtzite as constituent parts of the Earth’s crust can play a major role in waste treatment. The properties of those minerals towards the behavior of chromium (sorption) were studied under the effect of changes of pH and contact time to treat the waste solution of toxic chromate. The total chromium species in the reaction system was determined using Cr51 as a simpler, faster and more accurate analytical tools. Concerning the effect of types of minerals, the synthetic ones, the results indicated that pyrrhotite and wurtzite were highly effective for the removal of chromate with almost 100 % sorption capacity as it was pH-independent, despite the presence of a degree of reductive ability of both minerals. While, it was 99 % at pH 8.5 and 28 % at pH 3 for pyrite and magnetite, respectively, which was pH dependent. The equilibrium adsorption capacities for chromium adsorption were 0.34 ± 0.15, 0.028 ± 0.01 and 4.27 ± 1.3 mg/g mineral for natural minerals pyrite, magnetite and synthetic one pyrhotite, respectively. However, it was found 117.7 ± 10.9 mg/g for synthetic mineral wurtzite. These results can be attributed to the redox power of oxide and sulfide minerals; magnetite and, pyrite used. For kinetic studies of chromium (VI) adsorption, non linear model approved that the reaction could be described based on pseudo-second-order kinetics in such simulated environmental heterogeneous systems.

Estimating accurate and precise strain in low-magnitude penetratively deformed rocks: Integrating forward strain modeling and natural data

Estimating grain-scale strain using commonly used strain methods from a low-magnitude penetratively deformed rock is typically fraught with uncertainties as the measured strain is influenced by the pre-deformed grain shapes and grain-scale strain partitioning. Therefore, developing kinematic and mechanical models of orogenic wedge evolution based on such strain data can be misleading without knowing how accurate and precise those data are. To determine accuracy we created five 2-D synthetic rock images and deformed them with known strain under pure shear, simple shear, and general shear. We generated 4160 strain ratio (Rs) and long-axis orientation (φ) data. To determine precision we calculated 2σ (95%) uncertainties in Rs and φ from 102 quartz-rich rocks in Sikkim and generated 977 uncertainty data. Results show that the shape matrix eigenvector and stereographic projection methods record the lowest root mean square error, mean absolute error, and 2σ uncertainty values suggesting they are the most accurate and precise, regardless of strain ratio and deformation types. However, the accuracy and precision of φ deteriorate at Rs < 1.5. For most accurate and precise results, using the above mentioned methods, we recommend a minimum of 100 and 75 markers for Rs < 1.5 and Rs > 1.5, respectively.

Analysis of the Effect of Coordination Number on Permeability of the Three-Dimensional (3D) Rock Model Using the Lattice Boltzmann Method (LBM)

Understanding the correlation between coordination number and permeability is crucial for predicting fluid flow behavior in hydrocarbon reservoirs. In this study, we investigated the influence of coordination number on permeability in three-dimensional (3D) rock models. The research methodology involved the creation of synthetic 3D rock models, incorporating pores networks with varying coordination numbers. Utilizing the Lattice Boltzmann Methods (LBM), a computational fluid dynamics approach, we simulated fluid flow through these synthetic rock models and quantified their permeability. Our findings demonstrated a strong dependency of permeability on the coordination number of synthetic rock models. The application of the Lattice Boltzmann Method (LBM) proved to be an effective tool for understanding fluid flow behavior in porous rock formations and can serve as a basis for further optimization of reservoir management strategies to maximize hydrocarbon exploitation.

Determination of meaningful block sizes for rockfall modelling

The determination of the so-called design block is one of the central elements of the Austrian guideline for rockfall protection ONR 24810. It is specified as a certain percentile (P95–P98, depending on the event frequency) of a recorded block size distribution. Block size distributions may be determined from the detachment area (in situ block size distribution) and/or from the deposition area (rockfall block size distribution). Deposition areas, if present, are generally accessible and measurable without technical aids. However, most measuring methods are subjective, uncertain, not verifiable, or inaccurate. Also, rockfall blocks are often fragmented due to the preceding fall process. The in situ block size distribution is (also) required for meaningful rockfall modelling. The statistical method seems to be the most efficient and cost-effective method to determine in situ block size distributions with many blocks within the whole range of block sizes. In the current literature, joint properties are often described by the lognormal and exponential distribution functions. Today, we can model synthetic rock masses on the basis of discrete fracture networks. They statistically describe the geometric properties of the joint sets. This way, we can carry out exact rock mass block surveys and determine in situ block size distributions. We wanted to know whether the in situ block size distributions derived from the synthetic rock mass models can be described by probability distribution functions, and if so, how well. We fitted various distribution functions to three determined in situ block size distributions of different lithologies. We compared their correlations using the Kolmogorov–Smirnov test and the mean-squared error method. We show that the generalized exponential distribution function best describes the in situ block size distributions across various lithologies compared to 78 other distribution functions. This could lead to more certain, accurate, verifiable, holistic, and objective results. Further investigations are required.

Acoustic monitoring of compaction in cohesive granular materials.

We study the transition from cohesive to noncohesive states of cemented granular materials (synthetic rocks) under oedometric loading, combining simultaneous measurements of ultrasound velocity and acoustic emission (AE: microseosmicity). Our samples are agglomerates made of glass beads bonded with a few percent of cement, either ductile or brittle. These cemented granular samples exhibit an inelastic compaction beyond certain axial stresses likely due to the formation of compaction bands, which is accompanied by a significant decrease of compressional wave velocity. Upon subsequent cyclic unloading-reloading with constant consolidation stress, we found the mechanical and acoustic responses like those in noncohesive granular materials, which can be interpreted within the effective medium theory based on the Digby's bonding model. Moreover, this model allows P-wave velocity measured at vanishing pressure to be interpreted as an indicator of the debonding on the scale of grain contact. During the inelastic compaction, stick-slip-like stress drops were observed in brittle cement-bonded granular samples accompanied by the instantaneous decrease of the P-wave velocity and AEs which display an Omori-like law for foreshocks, i.e., precursors. By contrast, mechanical responses of ductile cement-bonded granular samples are smooth (without visible stick-slip-like stress drops) and mostly aseismic. By applying a cyclic loading-unloading with increasing consolidation stress, we observed a Kaiser-like memory effect in the brittle cement-bonded sample in the weakly damaged state which tends to disappear when the bonds are mostly broken in the noncohesive granular state after large-amplitude loading. In this paper, we show that the macroscopic ductile and brittle behavior of cemented granular media is controlled by the local processes on the scale of the bonds between grains.

Numerical Investigation for the Effect of Joint Persistence on Rock Slope Stability Using a Lattice Spring-Based Synthetic Rock Mass Model

This study underscores the profound influence of rock joints, both persistent and non-persistent with rock bridges, on the stability and behavior of rock masses—a critical consideration for sustainable engineering and natural structures, especially in rock slope stability. Leveraging the lattice spring-based synthetic rock mass (LS-SRM) modeling approach, this research aims to understand the impact of persistent and non-persistent joint parameters on rock slope stability. The Slope Model, a Synthetic Rock Mass (SRM) approach-based code, is used to investigate the joint parameters such as dip angle, spacing, rock bridge length, and trace overlapping. The results show that the mobilizing zones in slopes with non-persistent joints were smaller and shallower compared to slopes with fully persistent joints. The joint dip angle was found to heavily influence the failure mode in rock slopes with non-coplanar rock bridges. Shallow joint dip angles led to tensile failures, whereas steeper joint dip angles resulted in shear-tensile failures. Slopes with wider joint spacings exhibited deeper failure zones and a higher factor of safety, while longer rock bridge lengths enhanced slope stability and led to lower failure zones. The overlapping of joint traces has no apparent impact on slope stability and failure mechanism. This comprehensive analysis contributes valuable insights into sustainable rock engineering practices and the design of resilient structures in natural environments.

Numerical analysis on the factors affecting post-peak characteristics of coal under uniaxial compression

The post-peak characteristics of coal serve as a direct reflection of its failure process and are essential parameters for evaluating brittleness and bursting liability. Understanding the significant factors that influence post-peak characteristics can offer valuable insights for the prevention of coal bursts. In this study, the Synthetic Rock Mass method is employed to establish a numerical model, and the factors affecting coal post-peak characteristics are analyzed from four perspectives: coal matrix mechanical parameters, structural weak surface properties, height-to-width ratio, and loading rate. The research identifies four significant influencing factors: deformation modulus, density of discrete fracture networks, height-to-width ratio, and loading rate. The response and sensitivity of post-peak characteristics to single-factor and multi-factor interactions are assessed. The result suggested that feasible prevention and control measures for coal bursts can be formulated through four approaches: weakening the mechanical properties of coal pillars, increasing the number of structural weak surfaces in coal pillars, reducing the width of coal pillars, and optimizing mining and excavation speed. The efficacy of measures aimed at weakening the mechanical properties of coal is successfully demonstrated through a case study on coal burst prevention using large-diameter borehole drilling.

Influence of mineral composition on thermal equilibrium state during laser perforation

Energy consumption during laser rock perforation is controlled by conductive losses and latent heats during the phase transitions of melting and evaporation. To understand then improve the efficiency of laser perforation, the influence of rock mineral composition on these processes is investigated, and a theoretical model of laser rock breaking under steady-state heat conduction is developed. The findings reveal that the melting properties of mineral components primarily control thermal equilibrium during laser perforation. The key minerals, namely feldspar, quartz, and clay, were used to study the melt response in both pure samples and synthetic rock composites composed of these minerals. When feldspar is dominant, the thermal equilibrium temperature remains stable after reaching the feldspar gas phase boundary. While in situations where quartz dominates, the thermal equilibrium temperature is slightly below the melting point of pure quartz. The findings highlight the relationship between laser rock perforation efficiency and melting properties of minerals.

Digital rock advances from a material point method approach for simulation of frame moduli and a sedimentary petrology-inspired method for creation of synthetic samples through simulation of deposition and diagenesis

We compare hydromechanical simulation results that use two alternative sources of 3D digital rock input: micro-CT analysis and “synthetic rocks” created by using a newly developed process simulation methodology that more rigorously reflects knowledge from sedimentary petrology compared with previous efforts. We evaluate the performance of these alternative representations using St. Peter Sandstone samples where “dry” static bulk modulus ( K) and shear modulus ( G) are simulated using a new extension of the material point method that resolves contacts using high-resolution surface meshes and considers three alternative contact modeling approaches: “purely frictional,” “fully bonded,” and “cohesive zones.” We evaluate the model performance on two samples from the data set with multiple static moduli measurements (sample 1_2: porosity 24.6 vol%, K 10.2–14.7 GPa, and G 11.6–14.0 GPa; sample 11_2: porosity 12.4 vol%, K 13.5–24.6 GPa, and G 12.8–17.9 GPa). Purely frictional results underpredict measured modulus values, whereas fully bonded results overpredict them. Measured values are most closely approximated by results with cohesive zones that consider sets of discrete spring-like features at contacts. In contrast, shear modulus results from finite-element model simulations on structured grids tend to be significantly greater than measured values, particularly for samples with &lt;18 vol% porosity. Permeability values from digital rock-physics simulations for the studied samples are within factors of 2–5 of conventional core analysis measurements (2860 and 58 mD for samples 1_2 and 11_2, respectively). We determine that the process modeling approach (1) accurately reproduces the measured rock microstructure parameters from thin-section analysis, (2) leads to simulation results for dry static moduli and permeability with accuracy comparable to simulations that use micro-CT samples, and (3) provides a rigorous basis for predicting diagenetically induced variations in hydromechanical properties over the range from unconsolidated sand to indurated rock.